7.4 Carburetor Engine, Will Not Start A Week Later.

[MonacoMike]

I have had the boat since 2010 and it has always started perfectly. It started just fine after winter layup. Several weeks ago it would not start after sitting for 10 days. It will start every day, just not after a week or more of sitting.

A quick shot of starting fluid fires it right up and it will start with no pumping all day and each of the following days until a week of sitting. I have pumped the heck out of it after sitting for a week and it seems dry as a bone.

What is wrong here?

Thanks for any advice,

MM

 

[hottoddie]

The fuel in the carb is evaporating will it sits over several days. If you pump the throttle there is no gas in the carb bowl to pump into the engine. Try this, before pumping the throttle crank the engine for about 5 seconds then pump the throttle 2-3 times then crank the engine it will start. This is completely normal for a marine engine with a carb.

 

[Dieseljeff]

If above doesn't work, remove fuel line from carb and place in a can. While cranking engine over check for fuel being pumped. If not, fuel pump may be toast.

Do you have the combo seawater fuel pump?

If that is the case get the numbers off the pump and check your local auto parts store. They can be ordered for around 60-65 bucks.

Jeff

 

[scoflaw]

Time to rebuild the carb, sounds like the needle and seat are gummed up. It wont run fine if it was the fuel pump, gas should not evaporate after week.

 

[1990-270-da-lover]

It's possible that the accelerator pump on the carb itself is dying. If you have the flame arrestor off and someone pumps the throttle, you should at least be able to hear the fuel being pumped into the carb barrels. It's the pump that puts fuel into the carb so that there is enough fuel to fire the engine on a cold start. That's the first place I'd look.

 

[hottoddie]

If above doesn't work, remove fuel line from carb and place in a can. While cranking engine over check for fuel being pumped. If not, fuel pump may be toast.

Do you have the combo seawater fuel pump?

If that is the case get the numbers off the pump and check your local auto parts store. They can be ordered for around 60-65 bucks.

Jeff

No matter where you buy a fuel pump for a baot make sure it is a "marine" pump with the small return hose fitting on it.

 

[hottoddie]

Time to rebuild the carb, sounds like the needle and seat are gummed up. It wont run fine if it was the fuel pump, gas should not evaporate after week.

Enough gas will evaporate in several days to cause a hard start. This is only true on carb engines. Fuel injected engines will not have this symptom. Every carbed boat in our yacht club needs to crank for several seconds after sitting for a week or more. Completely normal.

 

[Jimmy Buoy]

It's possible that the accelerator pump on the carb itself is dying. If you have the flame arrestor off and someone pumps the throttle, you should at least be able to hear the fuel being pumped into the carb barrels. It's the pump that puts fuel into the carb so that there is enough fuel to fire the engine on a cold start. That's the first place I'd look.

+1 You should actually be able to see fuel squirting into the carb but you will have to pry open the choke plates with your fingers but hold with a screwdriver just in case it back fires. If no squirt its either a shot accelerator pump or the fuel supply is being totally cut off. There is often a small screen type filter in the carb where the fuel line connects. If you're taking off this line to check for fuel flow while cranking the engine, don't forget to pull this little screen filter out and check for debris!

 

[sdarc]

If the carb is a Rochester then there are plugs in the bottom of the float bowls that are leaking. These carbs are famous for this. Need to rebuild and seal them up.

 

[PlayDate]

It's possible that the accelerator pump on the carb itself is dying. If you have the flame arrestor off and someone pumps the throttle, you should at least be able to hear the fuel being pumped into the carb barrels. It's the pump that puts fuel into the carb so that there is enough fuel to fire the engine on a cold start. That's the first place I'd look.

Based on the symptoms and the history of easy starting.....this should be the right answer. The accelerator pump is used to provide additional fuel for starting and acceleration in cars. On boats, the only purpose they serve is to assist in starting the engine. If the pump diaphram is ruptured, no fuel will be sent into the manifold to assist starting. Rebuilding the carb or replacing it should solve the problem.

I usually replace the fuel pump at the same time of a carb rebuild/replacement just because it also operates on a diaphram which usually ruptures when you are using your boat resulting in the loss of fuel pressure.

John

 

[Bob & Sue]

Mike,
I had the same type problem you are when we bought ours 3 yrs ago even though we have different engines & carbs this might pertain to you also in troubleshooting it's Merc service bulletin 97-8.
My carb's electric choke was set 2 notches leaner than it should have been, I re-adjusted the carb and set the electric choke to 1 notch richer than merc recommends.
Since I made the changes the boat can sit for 3-4 weeks, 1 pump of the throttle it fires right up now, it does run a little rich at startup but it only lasts a couple minutes before it warms up and choke is off.
I'll email the service bulletin to you if you pm me an email to send it to, it has a checklist to go through your carb that might be helpful with illustrations on choke & carb settings recommended by mercruiser.
Good Luck

 

[moparlvr4406]

It's possible that the accelerator pump on the carb itself is dying. If you have the flame arrestor off and someone pumps the throttle, you should at least be able to hear the fuel being pumped into the carb barrels. It's the pump that puts fuel into the carb so that there is enough fuel to fire the engine on a cold start. That's the first place I'd look.

Respectfully disagree with this one...if the acc pumps were bad it would have a stumble on acceleration out of the hole or to plane

If the carb is a Rochester then there are plugs in the bottom of the float bowls that are leaking. These carbs are famous for this. Need to rebuild and seal them up.

IMO 100% on the mark...and most kits come with a dense foam seal that looks like an hour glass that fits into the cavity where these plugs sit to keep the fuel from draining into the manifold causing a hot flood or hot soak condition....sometimes you can just put the foam seal in and a tad bit of hi temp rtv over the plugs and cure the issue without a rebuild.

 

[1990-270-da-lover]

Respectfully disagree with this one...if the acc pumps were bad it would have a stumble on acceleration out of the hole or to plane
I forgot that the pump also aids in acceleration. Thanks for reminding me, that's why I love this site, the problem brainstorming is second to none, and I'm sure helps everyone.

 

[Dieseljeff]

It is!

http://www.amazon.com/Airtex-60932-Mechanical-Mercruiser-Cylinder/dp/B002HTYRD8

Jeff

 

[Dieseljeff]

Respectfully disagree with this one...if the acc pumps were bad it would have a stumble on acceleration out of the hole or to plane

IMO 100% on the mark...and most kits come with a dense foam seal that looks like an hour glass that fits into the cavity where these plugs sit to keep the fuel from draining into the manifold causing a hot flood or hot soak condition....sometimes you can just put the foam seal in and a tad bit of hi temp rtv over the plugs and cure the issue without a rebuild.

Boom there it is.....

Secondary Well Plug Fix Q1742/3

Source: http://quadrajetparts.com/rochester...quadrajet-rebuild-kit-marine-q4016-p-415.html


Replacing the original secondary well plugs on Rochester Quadrajets with our o-ringed plugs is a quick and easy way to fix a common problem plaguing most Quadrajets.

If you have to crank your engine over alot to start your engine after it has sat overnight, you probably have leaking secondary well plugs. This issue is very common with Rochester Quadrajets and now its easy to fix!

Other ways people have tried to seal the leak:

Putting epoxy on top of factory well plugs does not seal the leak, Tapping well bore and installing pipe plug with epoxy does work, but its alot of work and what happens if you use too much epoxy and it plugs or restricts the secondary passages?? Do it once and do it right, use our O-Ringed plugs.

How to Install Secondary Metering Well Stop Plugs-

1965-1968 Quadrajets with cup plugs- (Q1742)

1.- Drill hole in center of plug, install sheetrock screw and pull plug straight out using auto body slide hammer or grab screw with pair of dykes pliers.

2.- Slightly chamfer plug well opening and ensure plug bore is clean and burr free.

3.- Apply light coating of engine oil to "O" ring and install. Throttle body will ensure plug cannot slip down when installed.



1968 and later Quadrajets with aluminum plugs- (Q1743)

1.- Remove factory installed well plugs by carefully filing off the "peined" casting around the diameter of well plugs until flush with top of well plug.

2.- Drill hole in center of plug, install sheetrock screw and pull plug straight out using auto body slide hammer or grab screw with pair of dykes pliers.

3.- Slightly chamfer plug well opening and ensure plug bore is clean and burr free.

4.- Apply light coating of engine oil to "O" ring and install. Throttle body will ensure plug cannot slip down when installed.

 

[MonacoMike]

To all of you, THANK YOU!!! This site is awesome. Already have my guys ordering in the parts.

MM

 

[Dieseljeff]

Funny thing is... (not really)
My carb does the same thing after sitting a while and I've verified it by pulling the line off to the carb and it takes several seconds of cranking to get the gas flowing.

It has a new fuel pump, filter and I have checked the anti-siphon valve at the tank and it's good.

I have a Carter/Weber/Edlebrock original carb AFB 9772.
Haven't heard of well plugs on this carb but I am waiting on an expert to verify.

I'll let you know the results.

Jeff

 

[IanBat]

Think I will be ordering a set of replacement plugs as well


Sent from my iPad using Tapatalk HD

 

[sdarc]

Funny thing is... (not really)
My carb does the same thing after sitting a while and I've verified it by pulling the line off to the carb and it takes several seconds of cranking to get the gas flowing.

It has a new fuel pump, filter and I have checked the anti-siphon valve at the tank and it's good.

I have a Carter/Weber/Edlebrock original carb AFB 9772.
Haven't heard of well plugs on this carb but I am waiting on an expert to verify.

I'll let you know the results.

Jeff

These carbs do not have the well plugs. But somehow they do leak into the intake and then the combustion chamber. I had one do this on a Chevy ZZ4 crate engine. Hydraulic and broke the rod on start up in my driveway. Engine had stopped with a valve open and the fuel dumped in. Hit the key later and instant bang, bang, bang... My engine builder found a flooded chamber on a big block. I haven't figured out why these do this. been going Holley ever since.

 

[OldSkool]

To all of you, THANK YOU!!! This site is awesome. Already have my guys ordering in the parts.

MM

Did you order the optional toaster oven /Geny combo.
Sorry man, had to bust it. Hope you get her fixed up.

I replaced all my fuel lines with synthetic hose and rebuilt my carb as the idle valve was stuck. Freaking fuel caused water to condense in the fuel bowl and corroded everything up internally.